December 2008

Contents

Lattice Listens

Q: Some of the Power Manager II devices offer I²C. How is it used?

A: The following Power Manager II devices have I²C functionality:

I²C can be used for many purposes, including:

Reading the analog voltages from the VMON pins. Each VMON or Voltage Monitor Pin is an analog input capable of measuring 0 to 6V on power rails or other analog signals. The VMONs have both a programmable voltage comparator and an A/D converter tied to them. The I²C can be used for polling the voltage, data-logging system health or a supply wandering out of spec.
Reading the status of the VMON comparator or reading to see if the trip point has been reached on any VMON input comparator.
Reading the internal voltage rails of the Power Manager II device, to check the levels of the supply voltages being used.
Reading digital inputs. The I²C port can read an input to see if it has been activated.
The I²C port can write to the input pins to start, stop or test a sequence.
Reading or writing outputs including HVOUT. Pins need to be defined for I²C for this first.
The I²C port can read and write outputs, including HVOUT (HVOUTs are MOSFET gate driver pins, used to ramp an external supply at a controlled rate with an N-channel FET).
Trimming can also be accomplished with the ispPAC-POWR1220AT8 device.

I²C adds flexibility to the Power Manager II architecture and expands the capabilities of the device. It allows simple interfacing with CPLDs, CPUs and small microcontrollers as well as FPGAs with I²C code written into them as part of a core.

I²C can be used for debug as well as part of the overall functional design. The Lattice Applications Engineering Team frequently asks users about I²C in their systems and encourages them to add a few resistors for pull-ups and two test pads so they can use I²C later in development, even if they do not have the software. This quick tip has opened up opportunities for users to be exposed to I²C functions and alleviated some board issues during debug.

Software Support

The PAC-Designer design tool provides an I²C Graphic Utility that allows read/write access to all the I²C register functions and I/Os with I²C features. It uses a Lattice ispDOWNLOAD Cable to talk I²C with a small circuit board add-on or buffer. The parallel cable is supported now, the USB cable will be supported in a future release of PAC-Designer. The ispPAC-POWR1220AT8 Evaluation Board offers this capability and allows the user to quickly test drive the product.

PAC-Designer I²C Graphic Utility

To Learn More

For further information, contact Lattice Technical Support or your local Lattice sales representative.